This invention relates generally to elevator systems. More particularly, this invention relates to a device for damping the vertical vibration levels of an elevator car.
Elevator systems often include a car and a counterweight that move in opposite directions within a hoistway. A hoist machine moves the car in the hoistway via a traction machine connected between the hoist machine and the car. The traction machine includes connection members, such as ropes or belts, which are commonly looped around a sheave on the car and support the car and the counterweight for movement up and down the hoistway.
In elevator system design, the ride quality of the car is an important element of elevator system quality. Improving the ride quality of the car improves passenger comfort within the car. The elevator car noise level, horizontal vibration level, and vertical vibration level are often used in the elevator industry to describe the ride quality of the car. With regard to vertical vibration of the car, two methods are commonly employed to reduce vibration levels. One is to remove the source of the vertical vibration, and the other is to damp the vibration before it reaches the car, and thereby passengers riding in the car.
Prior vibration damping devices are well known in the art. For example, dampers arranged between the top of an elevator car assembly and a drive assembly commonly employ springs to improve the ride quality of the car. However, prior vibration dampers provide constant spring stiffness regardless of the load of the car, for example empty, half load or full load. In other words, prior dampers are linear. Because the vertical vibration level, and thereby the ride quality of the car, is a function of both spring stiffness and mass of the car, linear vibration dampers are disadvantageous for optimizing vibration damping capability for the varying car loads found in virtually every elevator system application.
In light of the foregoing, the present invention aims to resolve one or more of the aforementioned issues that afflict elevator systems.